In one aspect this invention relates to curable compositions. In another aspect this invention relates to radiation-curable addition polymers having pendant acryloyl unsaturation. In yet another aspect this invention relates to water-soluble radiation-curable addition polymers having pendant acryloyl unsaturation.
Curable compositions are often useful as protective and/or decorative coatings, paper coatings, etc. Photocurable coatings are especially useful in the preparation of photo-imagable printing materials such as photo-resists and lithographic plates.
Compositions which are curable or polymerizable by virtue of the presence of acryloyl unsaturation are well known in the prior art. However such prior art compositions often exhibit deficiencies in various physical properties which make them undesirable for certain practical applications. The most common deficiency of the prior art compositions is that they are generally not water soluble and thus often require the use of organic solvents for the deposition of a curable film or layer. Further, in the case of photo-imagable coatings of such compositions, organic solvents, which are expensive or flammable or toxic, are generally required to dissolve the unexposed portion of the coating from the cured image forming portion.
While the requirement of an organic solvent in the formation of a curable coating or film from a water-insoluble composition can in some applications be eliminated or minimized by deposition of the curable coating composition from an aqueous emulsion or dispersion, problems with stability of such emulsions or dispersions over time and under various storage conditions often arise. Thus additives such as emulsifiers and dispersing agents are generally required for the initial formation and the stabilization of such aqueous emuslions or dispersions. Furthermore, photo-imagable printing materials made by deposition of a film of a water-insoluble photo-imagable composition from an aqueous emulsion or dispersion still generally require the use of organic solvents to develop the imaged coating (i.e., to dissolve the unexposed portions) after exposure through a negative to crosslink and thereby insolubilize the exposed portions.
Polymers having pendant unsaturated quaternary nitrogen moieties have been reported. See, for example, Jones et al., Journal of Applied Polymer Science, Vol. V, No. 16, Pages 452-459 (1961) and Dzhalilov et al., Uzb. Khim. Zh., 18(1), Pages 56-59 (1974). However, such prior art polymers do not appear to be suitable as the photo-curable layer of photo-imagable articles by virtue of relatively slow photo-polymerization of the pendant vinyl groups there involved.
Water-soluble photo-imagable compositions have been reported. See, for example, U.S. Patents 3,628,963; 3,794,494; and 3,801,328. However, such prior art water-soluble curable compositions are often less than totally satisfactory as photo-imagable printing materials by virtue of excessive light exposure requirement. In addition, such compositions often exhibit relatively limited water solubility so that long development times, large amounts of water and/or the use of heated water in the development process are required.
Another problem encountered with some of the prior art curable coating compositions (both water soluble and water insoluble) is that, after curing, the coatings thus formed are brittle. This often leads to cracking, crazing, chipping or peeling of the coating when the coated substrate is thermally expanded and contracted and when the coated substrate is impacted with other articles.
Other problems encountered with prior art curable compositions (particularly in photo-imagable printing applications) include (a) poor photosensitivity, (b) slow cure times, (c) liquidity or tackiness of the uncured compositions, (d) gradual embrittlement of the cured and uncured compositions during storage at normal room humidities, (e) distortion of small features (which receive only small radiation doses during exposure through a negative) by virtue of swelling during the developemnt (i.e., washout) process, (f) excessive drying time requirements after development of imaged articles, and (g) poor adhesion of coatings to substrate.
In view of the aforementioned deficiencies with the prior art coating compositions, it would be highly desirable to provide curable coating compositions which are either water soluble or which form stable aqueous dispersions or emulsions without the need for separate dispersing agents or emulsifiers (i.e., which are at least inherently water dispersible). Further it would be highly desirable to provide curable compositions which are initially flexible and resilient and which retain their flexibility and resiliency (before and after curing) during prolonged storage at various humidities. In addition, it would be highly desirable to provide curable compositions (a) which feature rapid cure times, (b) which are not tacky prior to curing, (c) which are readily developed with water or dilute aqueous alcohol solutions after exposure of a film of such composition through a negative, (d) which do not swell during development of the exposed image, (e) which possess fast drying characteristics, and (f) which exhibit good adhesion to a variety of potential substrate materials.